The present invention relates to the field of gas chromatography and particularly relates to a device for positioning and holding one or more lengths of gas chromatographic columns subjected to one or more jets of fluids impinging on one or two spaced apart areas on said column length to change the temperature in this/these area/s.
The device can be particularly applied for the so-called modulation in the comprehensive two dimensional gas chromatography (GC×GC). An example of such a modulator is set forth in the International Application WO 02/39106 in the name of the Applicant, in which two jets of CO2, which are spaced apart from each other and controlled to act in an alternate manner, impinge on two separate areas in a column length being subjected to modulation. Another type of modulator is also known (WO 03/079001 in the name of the Applicant), in which one jet of CO2 impinges on an individual area in the column length. Other exemplary modulators for two dimensional gas chromatography are provided by the International Applications WO 01/51179, with two jets, and WO 03/082427 with an individual jet, both in the name of Zoex.
In any case, there arises the problem of having the gas chromatographic column length, or better, the impingement area/s of the jet/s, in a stable and univocally defined position relative to this/these jet/s, by avoiding any undesired movement of the column length and mainly avoiding vibrations in the column length under the action of the jet/s which may result in damage to the column and/or be detrimental to the effectiveness of modulation.
To solve these problems, according to the prior art, two bushes or ferrules are used, which are fastened to the ends of the column length and are elastically biased away from each other to tension the column length. Normally, for example in the practice of the application WO/023906, one of the two bushes or ferrules is fixed inside the gas chromatographic oven and the other is mounted on a slide which is biased by an adjustable spring in a direction away from the first one. Sometimes, this tensioning is not sufficient to stop the vibrations in the column length and an additional intermediate support is then provided.
This known solution, however, is not completely satisfying, as the column is stressed by the tensioning, the replacement or displacement of the modulation length are very laborious and the response of the tension spring changes over time because of the thermal cycles to which it is inevitably subjected.
Other solutions, which are generally applied with one or more jets focused on an individual spot and with a non-rectilinear column length, provide for a housing plaque in which the capillary column is fixed and arranged in coils, one or more coils thereof protruding from said plaque only in the area subjected to the jets.
This solution, however, does not allow replacing the capillary inside the support.